GB871325A - Device for visibly ascertaining the position of the weft threads in travelling cloth strips and for controlling weft straightening equipment - Google Patents

Abstract

871,325. Automatic control systems for moving webs. MAHLO, H. April 20, 1959 [April 26, 1958], No. 13449/59. Class 38 (4). [Also in Groups VIII and XL (b)] The lay of the weft threads in a moving fabric is detected by shining light through the fabric to a photo-electric cell formed with an elongated light aperture, the alternating component imparted to the cell output as the threads interrupt the light having a maximum amplitude when the threads lie parallel to the aperture. The width of the cell aperture is made the same as the thickness of a thread or the gap between two adjacent threads. The cell output may control automatic weft straightening apparatus. In one way of carrying out the invention, Fig. 6, two stationary cells 14 and 15 are disposed at equal and opposite angles to the normal weft direction and apply their outputs through amplifiers 16, 17 and rectifiers 19, 20 to a differential circuit 23, 24 controlling a polarized relay 25. With the weft in the normal direction the cell outputs are equal and the relay occupies its neutral position. Skew of the threads in either direction causes operation of the relay in the corresponding direction. Skew and bow of weft threads may be detected, Fig. 7 (not shown), by the use of two detecting arrangements somewhat similar to that shown in Fig. 6, one adjacent each selvedge. The outputs of the two detectors are applied in the same polarity to a first differential circuit so as to produce a response only when the two outputs are of like polarity, so indicating skew, and are applied in relatively reversed polarity to a second differential circuit so as to produce a response only when the two outputs are of different polarity, so indicating bow. A number of detecting arrangements according to the invention suitably inclined to normal weft direction may be disposed across the width of the fabric and may control apparatus to introduce a desired bow to the weft threads when the fabric enters a tentering frame in order that the fabric may leave the frame with straight threads, Fig. 11 (not shown). Automatic control is preferably effected by detectors at both the input and output of the frame. An alarm system is provided, Fig. 12 (not shown), when weft distortion exceeds the limit that may be converted automatically. The Specification discusses a number of auxiliary features including automatic gain control of the photo-electric cell amplifiers, Fig. 10 (not shown), an arrangement for translating the detector output into impulses the repetition frequency of which increases with the amplitude of detector signal, Fig. 8 (not shown), and the use of electrical bias to obtain an effect equivalent to varying the inclination of the detecting cells.